I have a Miramar and have NEVER had this happen. I don't have full body slide but it still should not be an issue. It sounds to me like your wipers on are working properly. Any water on the slide sides or top should be squegeed off by the rubber surrounding the slide. I would suggest calling the dealer and seeking there help on this.
The slide toppers ONLY purpose is to prevent debris from gathering on top the slide and getting caught in the rubber upon retracting the slide...causing the slides to leak. If the rubber seals/wipers are dry and not flipping to remove the water they may need to be lubricated, but this should be a dealer issue on a new motorhome.
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